Inside helmet sight display apparatus

ABSTRACT

Helmet mounted display apparatus in which a reflective inside surface of a partially transparent visor is used as the primary optical element. A paraboloidal inside visor surface coated with a metallic film may be used. A light source image or a virtual image is positioned at the focal point of the inside surface of the visor. The outside surface of the visor may be coated with an anti-reflective coating.

BACKGROUND OF THE INVENTION

The present invention is in the field of head or helmet mounted reticleand display systems. More specifically, it is a system which provides animage superimposed on the normal field of view of an observer to whosehead is has been attached. It is particularly suited to reconnaisance orweapons-aiming applications.

Prior art visual indicating or display systems are typified by thesystem disclosed in U.S. Pat. No. 3,291,906 to J. J. Ward et al. In thefigure of the Ward et al. patent, a multiple gun cathode ray tube isused as source together with a collimating lens system and planar beamsplitter. The planar beam splitter is placed in the pilot's line ofsight so that the image from the cathode ray tube may be superimposed onthe normal scene observed by the pilot.

In prior art development of a system in which these optics may behead-mounted, the cathode ray tube and heavy collimating lenses havebeen placed in a cylinder and mounted on either the right or left sideof the pilot's helmet. This lopsided weight placement is a considerabledisadvantage from the pilot's standpoint.

Furthermore, the combiner traditionally used is a small planar eyepieceplaced in close proximity to the pilot's eye. This eyepiece is aconsiderable distraction to some pilots. The close proximity of theeyepiece to the pilot's eye has also been shown to cause pilot anxiety.

Since the prior art uses a beam splitter in combination with collimatingoptics, the field of view is limited severely by the size of thecollimating optics. By using the inside surface of a head-mounted visoras the primary optical element, the field of view of the helmet mounteddisplay apparatus may be significantly increased.

Another disadvantage of prior art helmet mounted display apparatus wasthat two complete sets of collimating optics were required in order toprovide a system utilizable with either eye. The present invention maybe used with either eye merely by simple adjustment.

Applicant's invention overcomes these prior art disadvantages byproviding a reflective surface on a semi-transparent visor as itsprimary optical element. The visor is symmetrical about the helmet'slongitudinal axis; therefore, no lopsided weight need be attached to thepilot's helmet. Secondly, because the pilots are accustomed to use of avisor and the visor edges are out of the field of view, the anxietycommon with the use of a small beam splitter located close to thepilot's eye is averted. Thirdly, since the primary element is a concavemirror, the field of view of the device may be larger. Finally, byplacing an adjustable source in the vicinity of the focal point of theinside visor surface the helmet mounted display may be used with eitheror both eyes.

It is therefore one important object of the present invention to providehead or helmet mounted display apparatus providing superimposed imagesfor either eye without adjustment of the combining surface.

A second important object of applicant's invention is to provide helmetmounted display apparatus whose presence in the pilot's line of sightwill not create a distraction to the pilot.

SUMMARY OF THE INVENTION

These and other objects are attained by the use of a partiallytransparent, partially reflective head-mounted visor, one surface ofsaid visor having a concave shape and a curvature capable of collimatinglight. The concave surface of the visor has a definable focal point. Thevisor is combined with light emitting means which are positioned so thatthe image projected by the light emitting means appears to come from thefocal point of the visor surface.

BRIEF DESCRIPTION OF THE DRAWING

The nature of the invention and distinguishing features and advantagesthereof will be more clearly understood from the following detaileddescription and accompanying drawings in which:

FIG. 1 is a conceptual drawing showing a side view of elements of aspecific embodiment of the present invention in which the light sourceor light emitting means is centered at the focal point of a visorsurface.

FIG. 2 is a conceptual drawing showing a side view of elements of anembodiment in which a mirror is used to place the virtual image of thelight souce at a parabolic focal point so that the visor may be mountedmore closely to the pilot's helmet.

FIG. 3 is a cross-sectional view of a helmet with an embodiment of thehelmet-mounted display apparatus utilizing the light source concept ofFIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, an observer's helmet 10, which may be aconventional aviation helmet of standard construction, is shown placedin close proximity to the inside surface 12 of a partially transparent,partially reflective visor. The term "visor," as used herein, refers toa face mask or frontal piece, typically used in conjunction with ahelmet, through which an observer views the ouside world while theobserver's eyes are protected from wind blast, foreign objects, andother hazards. The curvature of visor 12 is such that the surface has adefinable focal point 14. The focal point of a reflective surface asused here may be defined as that point from which rays emanating outwardand striking the surface are reflected back parallel to one another.Stated another way, the focal point may be defined by the point ofconvergence of a band of rays which strike the surface parallel to itsaxis. A paraboloid of revolution has been used in one embodiment of theinvention, but a spherical or other concave surface with corrected lightsource could also be used.

Although the embodiments described here each use a helmet as a means forfixing the visor with respect to the observer's head, any mounting meanswhich allows the visor to move in consonance with normal head movementsof an observer so that the angular relationship between the head andvisor is preserved, would be acceptable for use in applicant'sinvention.

Affixed to surface 12 in attachment area 16 is a light emitting means orlight souce 18. Light source 18 is a light emitting object of smalldiameter which projects an information-containing image onto the visorsurface 12. The light source 18 is positioned so that it projects fromthe visor focal point 14. The projected image might, for example,consist of a retical pattern used in combination with a weapon slaved indirection to the pilot's line of sight. Another possible image is theoutput of a low light level TV system or other visual aid which could becarried to the source 18 utilizing a fiber optics bundle. Regardless ofits image information, light emitting source 18 shown is held rigid withrespect to the visor surface 12 by a structural member 22 attached tothe light source 18 and the attachment area 16 at opposite ends. Anillustrative ray 24 is shown emanating from the light emitting source18, striking the visor surface 12, and rebounding parallel to the axisof the visor surface.

The visor surface 12 will be coated with a reflective substance such assilver by vapor deposition. Although metallic films have been used inone embodiment of the invention, reflective coatings of any type areusable and metallic oxide coatings have been found satisfactory. Acoating of appropriate density, known to those skilled in the art, willmake the visor surface into a combining surface since it will bepartially reflective and partially transparent. With the light sourcecentered at the focal point, rays emitted from it will strike thereflective surface and a portion of them will be reflected substantiallyparallel to the axis of the visor surface.

Thus to an observer wearing the helmet 10, the image projected from thelight emitting source 18 will appear superimposed on the scene he viewsthrough the visor and will appear to be located at infinity due tosubstantial parallelism of the reflected rays. For light sources ofsmall area, that is, small displacement of the edges from the focalpoint of the surface 12, the eye will integrate out the slightnon-parallel effect associated with not being located exactly at thefocal point. Therefore a clear image of a reticle or a displayed objectsuperimposed at infinity on the outside scene will be visible.

FIG. 2 shows a slightly altered embodiment of applicant's invention. InFIG. 2, the observer's helmet 10 is located more closely to the visorsurface 12. This is possible because of a change in the construction ofthe light emitting means.

A practical difficulty may occur in the use of the embodiment of FIG. 1if it is desirable to make the visor stowable, that is, removable from apilot's line of sight. The reason for this possible difficulty is thatthe visor surface does not closely conform to the approximatelyspherical surface of the observer's helmet 10. In the embodiment of FIG.2, the focal point 14 is in actuality located in the space occupied bythe observer's forehead. In this embodiment, the light emitting means 28is hingedly attached to a clevis 30 which is connected to the visorsurface 12.

The light emitting means 28 in FIG. 2 has an extension 32, one end ofwhich is attached to the light emitting means 28. Th extension is in thedirection of the longitudinal axis of the light emitting means 28. Theopposite end of extension 32 holds a mirror 34. Mirror 34 is positionedsuch that the virtual image of an object displayed by the light emittingmeans 28 will be located at the focal point 14. The mirror 34, althoughplanar in the preferred embodiment, need not necessarily be planar. Itmay have magnification power to increase the image size.

The technique of displacing the light emitting means from the focalpoint and utilizing a mirror to locate the virtual image at the focalpoint permits placement of the visor surface 12 much closer to thehelmet than is the case with the embodiment figure shown in FIG. 1.Therefore, a track and visor shield making the visor retractable may bemore easily incorporated into the helmet structure.

A visor suitable for use in this invention may be fabricated utilizingany highly transparent durable material. If constructed of a plasticsubstance, the visor may be either machined, cast or injection molded.As previously stated, in its preferred embodiment the visor will haveits interior surface coated with a metallic oxide material making it acombiner. Additionally, use of a suitable anti-reflection or anti-glarecoating on the outside convex surface of the visor has been shown toimprove the performance of the applicant's invention.

The light emitting means 18 may project the image of either a reticlepattern or some other visual display. The most practical utilization ofthis system envisioned by the applicant is either a weapon sightingsystem or as an airborne reconnaissance system. In such applications, itmay be used in conjunction with a helmet position sensing system of thetype shown in U.S. Pat. No. 3,375,375 to R. Abbey et al. whichdetermines the direction in which a pilot is looking, and may eithertrain a weapon system, a camera or low light level television system inthat direction.

In operation, in either of these two uses, the applicant's inventionprovides an image focused at infinity and superimposed upon the scene atwhich the pilot is looking. In the reticle application, the presentinvention essentially takes the place of the sight 28 shown in FIG. 1 ofthe Abbey et al. patent.

The display generated by the light emitting means of the presentinvention is centered at the focal point of the visor surface 12 sincethe characteristic of the visor surface 12 is to collimate light comingfrom the focal point. The light striking the visor surface and beingreflected from it will be collimated and will thus appear superimposedat infinity on distant objects the observer views.

There is, of course, a limitation on the size of display which may beused with the visor surface. Because the display has a finite area,portions of it can certainly not be located at the focal point of thevisor surface. If the display is made sufficiently small, as previouslymentioned, the observer's eye integrates out the optical errors causedby the fact that the display is centered at the focal point, not locatedthere.

In FIG. 3 there is shown a detailed cross-sectional view of a preferredembodiment of the applicant's invention. An observer's helmet 10 has avisor 36 with an inner concave surface 37 and an outer convex surface38. The inner surface 37 may be coated with a metallic film to make itpartially reflective. The preferred shape of the inner concave surface37 is a paraboloid of revolution. The outer convex surface 38 ispreferably coated with anti-reflective or non-glare type coating.

Rigidly attached to the visor surface is a clevis 40, to which acylindrical light emitting means 42 is hingedly affixed. The lightemitting means is hinged on the clevis so that it may fold toward thevisor during visor retraction. The cylindrical light emitting means 42has an adjustment collar 44 which may be used to adjust the orientationof a planar mirror 48 attached to the light emitting means 42. Theplanar mirror 48 is positioned so that light striking it from the lightemitting means 42 will appear to be located at the focal point of theparaboloid of revolution which is the curvature of surface 36.

The visor is retractable by means of an offset member 50 which isconnected through a mechanical coupling arrangement to the visor 37.Another portion of the offset member 50 is connected to a visor stowingknob 52. The edges of the visor (not shown) may be placed in a groovedtrack (not shown) of Delrin or other suitable material located between aprotective overlay 54 and the pilot's helmet 10. A slot in the overlay54 is provided so that the pilot stowing knob may be used to pull thehelmet upwards, sliding it on the track. The light emitting means 42 isspring loaded so that when it contacts the edge of the helmet 10 itfolds towards the surface 37 for stowage.

Thus it is apparent that there has been provided, in accordance with theinvention, head mounted display apparatus that fully satisfies theobjects, aims, and advantages set forth above. While the invention hasbeen described in connection with specific embodiments thereof, it isevident that many alternatives, modifications, and variations, will beapparent to those skilled in the art in light of this description.Accordingly, it is intended to embrace all alternatives, modificationsand variations falling within the spirit and broad scope of the appendedclaims.

I claim: .[.1. A head-mounted display system comprising: appears to comefrom said focal point..]. .[.2. The apparatus as defined by claim 1 andmeans for mounting said visor in a fixed geometrical relationship to anobserver's head, so that said visor may move in consonance with theobserver's head movements..]. .[.3. The apparatus of claim 2 whereinsaid surface is defined by a paraboloid of revolution..]. .[.4. Theapparatus of claim 2 wherein the light emitting means includes a lightsource centered at said focal point..]. .[.5. The apparatus of claim 2wherein the light emitting means includes a light source and a mirrorconfigured so that the virtual image of the source is centered at saidfocal point..]. .[.6. Visual display apparatus, which comprises:a. avisor having an inner concave parabolic surface which is partiallyreflective and partially transparent, said visor being of sufficientsize to shield the eyes and forehead of an observer; b. a helmet towhich the visor is mounted in such a manner that an observer wearing thehelmet may have his eyes shielded by said visor; and c. light emittingmeans, fastened to the concave visor surface, for projecting an imagewhich is centered at the focal point of the concave visor surface..]..[.7. The apparatus of claim 5 wherein said light emitting meansincludes a light source and a substantially planar mirror placed at apredetermind angle to said light source..]. .[.8. The apparatus of claim2 wherein the visor has a substantially spherical curvature..]. .Iadd.9. A head-mounted display system comprising: a. a partially transparent,partially reflective visor, one surface of said visor having a curvaturefor collimating light, the curvature having a definable focal point; b.light emitting means position so that light travels from said means to areflective surface which is located out of the observer's normal forwardline of sight, the light being reflected from the reflective surfacedirectly, and without being further reflected, to the one surface of thevisor where the light is collimated and at least partially reflected tothe observer generally along the observer's normal forward line ofsight, the observer thus receiving the light as if it were originatingat infinity. .Iaddend..Iadd.
 10. The apparatus of claim 1 wherein saidlight emitting means is centered at said focal point. .Iaddend.